Continuous polymerization reactor

ABSTRACT

In a reactor for continuous polymerization in which an olefinic monomer is polymerized by contacting the olefinic monomer under suitable reaction conditions with an initiator, the formation of residue in the reactor is reduced by introducing the olefinic monomer and initiator into opposite sides of a turbulent zone produced by an agitator in the reactor. This improves mixing of the olefinic monomer and the initiator and prevents the initiator from contacting high concentrations of the olefinic monomer which results in reduced residue formation in the reactor.

This invention relates to continuous polymerization. In one aspect thisinvention relates to a reactor for a continuous polymerization process.In another aspect this invention relates to a method for reducing gelformation in a continuous polymerization process.

Continuous polymerization of olefinic monomers to form polymers is wellknown. In general, the polymerization process is intiated by contactingthe olefinic monomer with a catalyst system, which is generally referredto as an initiator, in a reactor. Monomer and initiator are continuouslyfed, generally with a solvent or diluent, to the reactor with thepolymer produced by the reaction of the monomer and initiator beingcontinuously removed from the reactor.

Continuous polymerization processes provide for more economic productionof polymer and more uniform compositions of the polymer than isgenerally possible with a batch process. However, it is well known thatin continuous polymerization processes there is a tendency for gel tobuild up in the reactor in which the monomer and initiator are contactedwhich results in fouling of the reactor. As used herein the term gelrefers to polymeric residue which is insoluble in the reaction mediumand coats the surfaces of the reactor which are in contact with thereaction mixture. In this context, the polymer may be insoluble becauseof extremely high molecular weight or it may be insoluble because ofcrosslinking side reactions which form a three-dimensional network inthe polymer analogous to the well known vulcanization of rubberypolymers.

It is thus an object of this invention to provide a reactor forcontacting monomer and initiator in a continuous polymerization processthe design of which results in reduced formation of gel in the reactor.It is another object of this invention to provide a method for reducinggel formation in the reactor in which monomer and initiator arecontacted in a continuous polymerization process.

In accordance with the present invention, olefinic monomer and initiatorare introduced with opposite sides of at least one turbulent zoneproduced by at least one agitator in a reactor. This improves mixing ofthe olefinic monomer and the initiator and prevents the initiator fromcontacting high concentrations of the olefinic monomer which results inreduced gel formation in the reactor in which the olefinic monomer andinitiator are contacted.

Other objects and advantages of the invention will be apparent from theforegoing brief description of the invention and the claims as well asfrom the detailed description of the process and drawing in which:

FIG. 1 is a side view of the reactor of the present invention with theoutside portion of the reactor being cut away;

FIG. 2 is a top view of one embodiment for an agitator; and

FIG. 3 is a top view of a second embodiment of an agitator.

The reactor is described in terms of a preferred reactor in which threeagitators are utilized. However, the invention is applicable to the useof any number of agitators which may be desired for a particular reactorconfiguration. The reactor is also described in terms of a particulararrangement of two different types of agitators. However, the inventionis applicable to any desired arrangement of agitators and is alsoapplicable to different types of agitators than those illustrated.

Referring now to the drawings and in particular FIG. 1, there isillustrated a vessel 11 which is utilized to confine the olefinicmonomer and initiator during the reaction. Any suitable configurationfor the vessel 11 may be utilized. Preferably, the vessel 11 consists ofa lower portion through which the conduits carrying olefinic monomer andinitiator enter and an upper portion from which polymer is removed. Thelower and upper portion are separated by a cylindrical portion in such amanner that the longitudinal axis of the cylindrical portion extendsthrough the center of the lower and upper portions. The upper portion ofthe vessel 11 is sealed by the plate 12. A drive shaft 14 extendsthrough the plate 12. The drive shaft 14 may be coupled to any suitabledrive mechanism such as an electric motor. Shaft 15 extends along thelongitudinal axis of the vessel 11 to a point closely adjacent thebottom of the vessel 11. The shaft 15 is operably coupled to the driveshaft 14 by the coupling mechanism 16. Three agitators 17, 18 and 19 arecoupled to the shaft 15. Preferably, the agitators 17, 18 and 19 areequidistantly spaced with the upper agitator 19 being spaced from thecoupling element 16 by the same distance as the upper agitator 19 isspaced from the middle agitator 18. Preferably, the agitator 17 is aradial agitator while the agitators 18 and 19 are axial agitators. Asused herein the term radial agitator refers to an agitator the blades ofwhich have no pitch with respect to the shaft 15. In contrast, as usedherein the term axial agitator refers to an agitator the blades of whichhave a pitch with respect to the shaft 15. Preferably, the pitch of theaxial agitators 18 and 19 is such that the turbulent zones produced aredirected towards the bottom of the vessel 11 to provide improved mixingof the monomer and initiator throughout the reactor which results inincreased conversion of monomer to polymer. The agitators 17-19 arerotated continuously in the same direction during the continuouspolymerization process. For the reactor of FIG. 1, the direction ofrotation is as shown by the arrow 20.

The arrangement of the agitators illustrated in FIG. 1 is preferredbecause the residence time in the reactor is increased over that whichcan be obtained with other agitator arrangements. The increasedresidence time results in higher monomer conversion.

Monomer is introduced into the vessel 11 through conduit means 21 whichextends through the bottom portion of the vessel 11 and along one sideof the cylindrical portion of the vessel 11 to a point above the top ofthe agitator 19. The only outlets for monomer from conduit means 21 areoutlet holes 23, 24 and 25. Monomer is released from outlet hole 23 intothe turbulent zone produced by the agitator 17. In like manner, monomeris released from outlet holes 24 and 25 into the turbulent zonesproduced by agitators 18 and 19, respectively. Initiator is introducedinto the vessel 11 through conduit means 31 which extends through thebottom portion of the vessel 11 and along a second side of thecylindrical portion of the vessel 11, which is substantiallydiametrically opposed to the first side, to a position above the top ofthe agitator 19. Again, the only fluid outlets from conduit means 31 areoutlet holes 33, 34 and 35. Initiator flows from the outlet hole 33 intothe turbulent zone produced by the agitator 17. In like manner,initiator flows from the outlet holes 34 and 35 into the turbulent zonesproduced by agitators 18 and 19, respectively.

The outlet holes for monomer and initiator may be located in any desiredmanner with respect to the turbulent zones which will allow introductionof monomer and initiator into each turbulent zone in the reactor.Preferably, the outlet holes for monomer and initiator are located at apont formed by the intersection of a line extending from the bottom ofthe blade portions of the agitators to the conduits for monomer andinitiator. Also, for maximum suppression of gel formation, the outletholes for monomer are substantially diametrically opposed to the outletholes for initiator in the vessel 11.

Other techniques could be used to introduce monomer and initiator intothe vessel 11 if desired. As an example, separate conduits could enterthe cylindrical side portion of the vessel 11 and open directly into theturbulent zones. The important factor is the introduction of monomer byany means into a first part of the periphery of a turbulent zone and theintroduction of monomer into a second part of the periphery of theturbulent zone, where the first part of the periphery is substantiallydiametrically opposed to the second side of the periphery.

To promote mixing of monomer and initiator in the vessel 11, fourbaffles spaced equidistantly around the circumference of the insidesurface of the vessel 11 are preferably utilized. The baffles arepreferably located substantially adjacent the sides of the cylindricalportion of the vessel 11. Only two baffles 41 and 42 are illustrated inFIG. 1. One of the remaining baffles is hidden by the shaft 15 and theother baffle has been cut away to illustrate the reactor more fully.

Baffles are not required in the reactor if adequate mixing can beobtained without the baffles. In most continuous polymerizationprocesses at least two baffles will be utilized to promote adequatemixing with four baffles being preferred.

The baffles in the reactor, of which baffles 41 and 42 arerepresentative, may be supported in any desired manner such as astandard baffle support ring (not illustrated). In like manner, theconduits 21 and 31 may be supported inside the reactor by any suitablemethod. Preferably, the conduits 21 and 31 are supported by the samebaffle support rings which support the baffles 41 and 42.

As has been previously stated, monomer and initiator are introduced intothe vessel 11 through conduit means 21 and 31, respectively. Also, as iswell known in continuous polymerization processes, solvents,randomizers, gel suppressants, couplers, stabilizers and other wellknown reactants may be introduced with the monomer or initiator. Thereaction mixture, of which polymer will form a major portion, is removedfrom the vessel 11 through conduit means 51 which extends through anupper portion of the vessel 11. The thus removed reaction mixture isprocessed as required by the specific continuous polymerization process.

Although not required, as a safety measure it is preferred to locate anadditional conduit 52 in an upper portion of the vessel 11 with conduit52 being connected to a safety blowout disc (not illustrated). Pressuregauges may also be associated with conduit means 52 with such pressuremeasurements being utilized to control the flow of reactants throughconduit means 51 in such a manner that a desired pressure is maintainedin the vessel 11.

Referring now to FIG. 2, there is illustrated a top view of the radialagitator 17. As is illustrated in FIG. 2, the radial agitator 17preferably has six blades 61-66. More or fewer blades may be utilized asdesired. The blades 61-66 are preferably rectangular plates althoughother geometric forms could be used if desired. Two sides of the blades61-66 preferably extend outwardly from the shaft 15 at substantially 90°angles. The blades 61-66 are aligned so as to be perpendicular to thedirection of rotation of the radial agitator 17 and thus a strongerturbulence and mixing effect is provided by the radial agitator 17 thanby the axial agitators 18 and 19. The turbulent zone is directedoutwardly towards the lower part of the cylindrical portion of thevessel 11.

Referring now to FIG. 3, there is illustrated a top view of theagitators 18 and 19 illustrated in FIG. 1. As is illustrated in FIG. 3,the agitators 18 and 19 preferably have three blades 71-73. The blades71-73 are preferably rectangular plates although other geometric formscould be used if desired. Two sides of the blades 71-73 preferablyextend outwardly from the shaft 15 at substantially 90° angles. Theblades 71-73 are aligned so as to have at least about a 15° pitch withrespect to the longitudinal axis of the vessel 11 and the shaft 15 witha 45° pitch being preferred. The direction of the pitch is such as toprovide a turbulent zone directed towards the lower portion of thevessel 11 at the pitch angle.

As has been previously stated, the reactor illustrated in FIG. 1 isapplicable to a large number of continuous polymerization processes inwhich it is desired to contact monomer and initiator to form polymer.The reactor is particularly applicable to the production of homopolymersor conjugated dienes or random copolymers of conjugated dienes and vinylaromatic compounds in solution polymerization processes.

Any suitable olefinic monomer may be contacted with any suitableinitiator in the vessel 11 under any suitable conditions to producepolymer. Specific olefinic monomers, initiator systems and reactionconditions are well known. As an example, U.S. Pat. No. 3,219,647, whichis hereby incorporated by reference, discloses suitable olefinicmonomers which may be used in continuous polymerization systems whichemploy the transition metal/organometal catalyst systems which aregenerally referred to as the Zeigler-type initiators. The reactionconditions may be the same as those described in U.S. Pat. No.3,219,647. It is noted that if the initiator system comprises two ormore components, the most convenient way for such initiator systems tobe utilized with the reactor illustrated in FIG. 1 is for the iniitatorcomponents to be premixed prior to charging to the reactor through theinitiator inlet conduit 31 illustrated in FIG. 1. In like manner, ifmore than one monomer is utilized or if a solvent, gel suppressant orother reactant is desired, it is preferred to mix the two or moremonomers and the additional reactants prior to introducing such mixtureinto the reactor illustrated in FIG. 1 through conduit means 21.

U.S. Pat. No. 4,091,198 discloses continuous polymerization of aconjugated diene with a monovinyl aromatic compound in the production ofrandom copolymers by organolithium initiation. The reactor illustratedin FIG. 1 is particularly applicable to the continuous polymerizationprocess described in U.S. Pat. No. 4,091,198 which is herebyincorporated by reference. The monomer and initiator introduced into thereactor illustrated in FIG. 1 may be those described in U.S. 4,091,198and the reaction conditions may be the same as those described in U.S.4,091,198.

The following examples are presented in further illustration of theinvention:

EXAMPLE 1

Polybutadiene was prepared in a continuous polymerization utilizing thereactor configuration illustrated in FIG. 1. The specific componentscharged to the reactor illustrated in FIG. 1 through the monomer inlet21 and the initiator inlet 31 are as follows:

    ______________________________________                                                        Parts by Weight                                               ______________________________________                                        Components Charged                                                            Through Monomer Inlet                                                         Butadiene         100                                                         Cyclohexane       475                                                         Tetrahydrofuran   0.04                                                        1,2-Butadiene     0.04                                                        Components Charged                                                            Through Initiator Inlet                                                       n-Butyllithium    0.065                                                       Cyclohexane       156                                                         ______________________________________                                    

Cyclohexane was utilized as a solvent for the butadiene, n-butyllithium,and for the polymer produced. Tetrahydrofuran was utilized as a promotorwhile 1,2-butadiene was utilized as a gel suppressant.

The turbine configuration was as illustrated in FIG. 1. The shaft 15 wasrotated at 350 rpm. The components charged to the monomer inlet and theinitiator inlet were introduced through the outlets 23, 24, 25 and theoutlets 33, 34 and 35, respectively. The continuous polymerizationprocess was continued for 151 hours at a reaction temperature of 131° C.At the end of 151 hours the wet polymeric residue in the reactor wasdetermined to occupy ten percent by volume of the reactor. The wetresidue was then removed and dried and it was determined that 50 partsper million of dry polymeric residue, based on throughput, had beendeposited in the reactor.

EXAMPLE 2

As a comparison, the reactor illustrated in FIG. 1 was modified in sucha manner that monomer was introduced into the central portion of thebottom of the reactor and initiator was introduced in the bottomperiphery of the reactor. Components charged through the monomer inletwere the same as in Example 1. Components charged to the intiator inletwere the same as in Example 1 except that the amount of n-butyllithiumwas reduced to 0.055 parts by weight which is not considered to be asignificant change with respect to the formation of polymeric residue inthe reactor.

The turbine configuration was as illustrated in FIG. 1 and the shaft 15was again rotated at 350 rpm. The continuous polymerization process wasrun for 90 hours and the reaction temperature was 126° C. At the end of90 hours, the wet polymeric residue in the reactor was determined tooccupy fifteen percent by volume of the reactor. The amount of dryresidue was not directly determined.

Comparing the results of Example 1 with Example 2 indicates that morepolymeric residue was formed in the continuous polymerization process ofExample 2 than in Example 1 even though the continuous polymerizationprocess of Example 1 was run for a substantially longer period of timethus illustrating that benefits which may be obtained by introducingmonomer and initiator into a reactor in accordance with the presentinvention.

EXAMPLE 3

Polybutadiene was prepared in a continuous polymerization utilizing thereactor configuration illustrated in FIG. 1. The specific componentscharged to the reactor through the monomer inlet 21 and the initiatorinlet 31 are as follows:

    ______________________________________                                                        Parts by Weight                                               ______________________________________                                        Components Charged                                                            Through Monomer Inlet                                                         Butadiene         100                                                         Cyclohexane       475                                                         Tetrahydrofuran   0.04                                                        1,2-Butadiene     0.04                                                        Components Charged                                                            Through Initiator Inlet                                                       n-Butyllithium    0.065                                                       Cyclohexane       156                                                         ______________________________________                                    

The turbine configuration was as illustrated in FIG. 1. The shaft 15 wasagain rotated at 350 rpm. The components charged to the monomer inletand the initiator inlet were introduced through the outlets 23, 24, 25and the outlets 33, 34 and 35, respectively. The continuouspolymerization process was continued for 502 hours at a reactiontemperature of 126° C. At the end of 502 hours the wet polymeric residuein the reactor was determined to occupy less than one percent by volumeof the reactor. The wet residue was then removed and dried and it wasdetermined that less than one part per million of dry polymeric residue,based on throughput, had been deposited in the reactor.

Reasonable variations and modifications are possible within the scope ofthe disclosure and the appended claims to the invention.

That which is claimed is:
 1. A reactor for contacting olefinic monomerand initiator in a continuous polymerization process, said reactorcomprising:a vessel, having an upper portion and a lower portion,wherein a longitudinal axis extends from said lower portion to saidupper portion; radial turbine means for creating a first turbulent zonein said vessel; a first axial turbine means for creating a secondturbulent zone in said vessel; a first conduit means extending from thelower portion of said vessel to the upper portion of said vesselsubstantially along a first portion of the wall of said vessel, whereinsaid first conduit means has a fluid outlet at the position of saidmeans for creating said first turbulent zone and at the position of saidmeans for creating said second turbulent zone; means for introducingsaid olefinic monomer into said first conduit means to thereby introducesaid olefinic monomer into the periphery of said first and secondturbulent zones; a second conduit means extending from the lower portionof said vessel to the upper portion of said vessel substantially along asecond portion of the wall of said vessel, wherein said second conduitmeans has a fluid outlet at the position of said means for creating saidfirst turbulent zone and at the position of said means for creating saidsecond turbulent zone, wherein said first portion of the wall of saidvessel is substantially diametrically opposed to said second portion ofthe wall of said vessel; means for introducing initiator into saidsecond conduit means to thereby introduce said initiator into theperiphery of said first and second turbulent zones; and means forremoving the reaction products from said vessel.
 2. A reactor inaccordance with claim 1 additionally comprising a second axial turbinemeans for creating a third turbulent zone in said vessel, wherein saidfirst conduit means has a fluid outlet at the position of said means forcreating said third turbulent zone and said second conduit means has afluid outlet at the position of said means for creating said thirdturbulent zone, wherein the olefinic monomer is introduced into theperiphery of said third turbulent zone through said first conduit meansand said initiator is introduced into the periphery of said thirdturbulent zone through said second conduit means.
 3. A reactor inaccordance with claim 2 wherein said upper portion of said vessel isseparated from said lower portion of said vessel by a cylindricalcentral portion and wherein said means for creating said first, secondand third turbulent zones in said vessel comprises:a shaft located onsaid longitudinal axis and extending from the upper portion of saidvessel to the lower portion of said vessel; a drive means for rotatingsaid shaft; means for coupling said shaft to said drive means; saidradial turbine means, having at least one blade, for creating said firstturbulent zone, wherein said at least one blade is a plate which isaligned so as to be substantially perpendicular to the direction ofrotation of said shaft; means for coupling said radial turbine means tosaid shaft at a position in the portion of said cylindrical portion ofsaid vessel which is substantially adjacent said lower portion of saidvessel; said first axial turbine means, having at least one blade, forcreating said second turbulent zone, wherein said at least one blade isa plate which is aligned so as to have a pitch of at least about 15°with respect to said shaft with the angle of the pitch being such as todirect said second turbulent zone towards said lower portion of saidvessel at the angle of the pitch; means for coupling said first axialturbine means to said shaft at a position in the central portion of saidcylindrical central portion of said vessel; said second axial turbinemeans, having at least one blade, for creating said third turbulentzone, wherein said at least one blade is a plate which is aligned so asto have a pitch of at least about 15° with respect to said shaft withthe angle of the pitch being such as to direct said third turbulent zonetowards said lower portion of said vessel at the angle of the pitch; andmeans for coupling said second axial turbine means to said shaft at aposition in the portion of said cylindrical central portion of saidvessel which is substantially adjacent said lower portion of saidvessel.
 4. A reactor in accordance with claim 3 wherein said radialturbine means and said first and second axial turbine means are spacedequidistantly on said shaft.
 5. A reactor in accordance with claim 4wherein said radial turbine means has six blades, wherein the six bladesof said radial turbine means are rectangular plates, wherein two sidesof each one of said six blades extend outwardly from said shaft atsubstantially 90° angles with respect to said shaft, wherein said firstaxial turbine means and said second axial turbine means have fourblades, wherein the four blades of said first and second axial turbinemeans are rectangular plates, wherein two sides of each one of the fourblades of said first and second axial tdurbine means extend outwardlyfrom said shaft at substantially 90° angles, and wherein the pitch ofthe four blades of said first and second axial turbine means is about45° with respect to said shaft.
 6. A reactor in accordance with claim 3wherein said reaction products are removed from the upper portion ofsaid vessel and wherein the fluid outlets in said first and secondconduit means are located at points formed by the intersection of linesextending substantially perpendicularly from said shaft along the bottomof said at least one blade, of said radial turbine means and said firstand second axial turbine means, to said first and second conduit means.